The present invention relates to radiation sensitive resist compositions which exhibit enhanced resistance to plasma and especially to Cl2/O2 plasma used in reactive ion etching. The present invention is concerned with the compositions as well as their use in lithography. For instance, the materials of the present invention are suitable for use in device and mask fabrication on optical, e-beam, x-ray and ion-beam lithography tools.
In the manufacture of patterned devices and especially microelectronic devices, the processes of etching different layers which constitute the finished product are among the most crucial steps involved. One method widely employed in the etching process is to overlay the surface to be etched with a suitable mask.
The mask is typically created by imagewise forming a pattern of resist material over those areas of the substrate to be shielded from the etching. The resist is normally formed of a polymeric organic material. The pattern is formed by imagewise exposing the resist material to irradiation by lithographic techniques. The irradiation employed is usually x-ray, UV radiation, or electron beam radiation.
Radiation sensitive materials and/or compositions are either positive-acting (i.e. radiation solubilizable) or negative-acting (i.e. radiation insolubilizable or crosslinkable). Positive-working sensitive compositions are rendered soluble (or developable) by exposure to radiation (UV light, x-ray or electron-beam) and can be removed using selective developing solutions leaving unexposed areas intact. Negative-working sensitive compositions are those which become insoluble upon exposure to actinic radiation. Selected solutions can dissolve and remove the unexposed areas of the composition while leaving the exposed portions intact. Development of such exposed materials yields negative tone images.
The production of binary masks includes pattern definition by exposure of electron beam resists on, for instance, a chrome coated glass plate. The image is then developed and the pattern is etched into chrome by either aqueous based wet etching or by reactive ion etching with a chlorine based plasma (see U.S. Pat. No. 3,236,413).
With the advent of shrinking dimensions, the photomask of nX enlargement (n-4-10X) is also shrinking to less than 400 nm in dimensions. Because wet etching causes undercutting or undesired enlargement, reactive ion etching (RIE) has been utilized (see Tsai et al U.S. Pat. No. 3,412,149). In RIE greater than 50% of the resist film can be eroded away. The particular resists that have been used for electron beam exposure are polymers that undergo main chain degradation. The primary examples are derived from a positive resist such as polymethylmethacrylate (PMMA) described in U.S. Pat. No. 3,535,137 and polybutene sulfone described in U.S. Pat. No. 3,935,332. Improved contrast developers for PMMA can be found such as amyl acetate as described, for example, in U.S. Pat. No. 3,931,435 and a mixture of methyl isobutyl ketone and water as described in U.S. Pat. No. 4,078,098. All of these resists and copolymers are described in W. Moreau, Semiconductor Lithography, Plenum Press, 1989, Chapter 3. These resists, however, are not RIE etch resistant and thus the pattern cannot be transferred by an RIE process.
For reactive ion etching, a commercial resist identified as ZEP manufactured by Nippon Zeon (see U.S. Pat. No. 3,236,397) has been used. ZEP is composed of a copolymer of alpha-chloromethacrylate and alpha-methyl styrene (PCMMS). Copolymers of polyalpha-chloromethacrylate are described in U.S. Pat. Nos. 4,359,481, 4,011,351 and 4,454,222. A preferred example is described in U.S. Pat. No. 4,259,407 which is directed to a copolymer of poly(alpha-chloroacrylate-alpha-methylstyrene), commercially available from Nippon Zeon as ZEP 7000 electron beam resist. U.S. Pat. No. 4,259,407 discusses a developer of a ketone such as 3 pentanone mixed with another ketone. In U.S. Pat. No. 4,454,222, a developer comprising MIBK (4 methyl-2-butanone) and isopropanol or a mixture with 2 butanone is suggested for a trifluoromethyl alpha-chloroacrylate-methacrylic acid copolymer in a spray development mode. U.S. Pat. No. 4,414,313 describes a mixture of dimethylacetamide and toluene as a developer for a poly(alpha-chloroacrylate-methacrylic acid) copolymer. The disclosures of U.S. Pat. Nos. 4,359,481, 4,011,351, 4,454,222, 4,259,407 and 4,414,313 are incorporated herein by reference.
The ZEP resist uses a commercial developer preferably consisting of the following compositions: ZED 300-methyl ethyl ketone/anisole 93/7 by weight, ZED 400-diglyme/methyl ethyl ketone 20/80 by weight, and ZED 500-diethyl ketone/diethyl malonate 50/50 by weight.
In addition to using ZEP type resists for chrome mask fabrication, other masks, substrates or direct exposure of silicon wafers could also be exposed and developed with the resist, exposure tools, and developer modes used in semiconductor fabrication.
After the resist is developed forming the desired mask, the substrate and mask can be immersed in a chemical solution which attacks the substrate to be etched while leaving the mask intact. These wet chemical processes suffer from the difficulty of achieving well-defined edges on the etched surfaces. This is due to the chemicals undercutting the mask and the formation of an isotropic image. In other words, conventional chemical wet processes do not provide the resolution considered necessary to achieve optimum dimensions consistent with current processing requirements.
Moreover, such wet etching processes are undesirable because of the environmental and safety concerns associated therewith.
In view of the various drawbacks associated with wet chemical development, various so-called xe2x80x9cdry processesxe2x80x9d have been suggested to improve the process from an environmental viewpoint, as well as to reduce the relative cost of the etching. Furthermore, these xe2x80x9cdry processesxe2x80x9d have the potential advantage of greater process control and higher aspect ratio images. Also, when fabricating patterns having feature sizes below 350 nm, dry etching processes are necessary.
Such xe2x80x9cdry processesxe2x80x9d generally involve passing a gas through a container and creating a plasma in this gas. The species in this gas are then used to etch a substrate placed in the chamber or container. Typical examples of such xe2x80x9cdry processesxe2x80x9d are plasma etching, sputter etching, and reactive ion etching.
Reactive ion etching provides well-defined, vertically etched sidewalls.
One of the challenges in the fabrication of microelectronic devices and masks is to develop a resist which exhibits good lithographic performance as well as high dry etch resistance for subsequent pattern transfer into an underlying substrate. The dry etch chemistries include O2 currently used for antireflective coatings, Cl2/O2 currently used for chrome etching in mask fabrication, Cl2 based plasma for polysilicon etch, and fluorocarbon based plasmas such as CF4 for oxide etching. These plasmas are examples only and are not meant to limit the scope. Conventional novolak/diazonapthoquinone resists used for i-line lithography have to date exhibited the best dry etch resistance. ZEP is an e-beam resist which has been adopted by the industry for advanced mask making to replace the conventional wet etch polybutenesulfone (PBS) process. Although ZEP provides significant improvement over the PBS process, its dry etch resistance to Cl2/O2 is marginal (etch rate of 1.95 nm/s). Novolac is 1.4 nm/s.
There is a need to develop radiation sensitive compositions that provide improved dry etch resistance for use in mask fabrication (binary, attenuating phase shift masks, alternating phase shift masks) and for device fabrication.
The use of silicon and germanium has been intended to impart O2 etch resistance to certain resist materials. For example, see U.S. Pat. Nos. 4,764,247, 4,935,094 and 5,733,706 and Microelectronic Engineering 3, 279 (1985). However, these do not suggest masking against Cl2/O2 reactive ion etching.
The present invention provides resist compositions which are sensitive to imaging irradiation while exhibiting enhanced resistance to reactive ion etching. Photoresist compositions of the present invention typically exhibit enhanced resistance to reactive ion etching using various plasmas including Cl2/O2 plasma, O2, Cl2 and fluorocarbons such as CF4. As would be understood by those skilled in the art, Cl2/O2 plasma refers to a plasma containing atomic Cl and O from the decomposition in the plasma of Cl2 and O2 species.
In particular, the resist compositions of the present invention comprise a radiation sensitive polymer and at least one organometallic compound.
The present invention also relates to resist compositions comprising a radiation sensitive polymer and at least one organometallic compound of at least one metal selected from the group consisting of yttrium, aluminum, iron, titanium, zirconium, hafnium and mixtures thereof.
The present invention also relates to a method for forming a pattern of a resist which comprises:
a) providing on a substrate a layer of a resist composition which comprises a radiation sensitive polymer and at least one organometallic compound;
b) imagewise exposing the layer of resist composition to irradiation; and
c) developing the resist to thereby form the pattern.
A further aspect of the present invention relates to forming a pattern on a substrate which comprises:
a) providing a layer to be patterned on a substrate,
b) providing on the layer to be patterned a layer of a resist composition which comprises a radiation sensitive composition and at least one organometallic compound,
c) imagewise exposing the layer of resist composition to irradiation,
d) developing the resist to form the desired pattern, and
e) subjecting the layer to be patterned to reactive ion etching with the resist acting as a mask to thereby form the desired pattern on the substrate.
A still further aspect of the present invention relates to method for forming a pattern of a resist which comprises:
a) providing on a substrate a layer of a resist composition which comprises a radiation sensitive polymer and at least one organometallic compound of at least one metal selected from the group consisting of yttrium, aluminum, iron, titanium, zirconium and hafnium and mixtures thereof;
b) imagewise exposing the layer of resist composition to irradiation; and
c) developing the resist to thereby form the pattern.
Another aspect of the present invention relates to forming a pattern on a substrate which comprises:
a) providing a layer to be patterned on a substrate,
b) providing on the layer to be patterned a layer of a resist composition which comprises a radiation sensitive composition and at least one organometallic compound of at least one metal selected from the group consisting of yttrium, aluminum, iron, titanium, zirconium and hafnium and mixtures thereof,
c) imagewise exposing the layer of resist composition to irradiation,
d) developing the resist to form the desired pattern, and
e) subjecting the layer to be patterned to reactive ion etching with the resist acting as a mask to thereby form the desired pattern on the substrate.
The present invention is also concerned with structures comprising a patterned layer thereon wherein the patterned layer comprises a radiation sensitive resist polymer and at least one organometallic compound.
A further aspect of the present invention relates to a structure comprising a substrate having a patterned layer thereon wherein the patterned layer comprises a radiation sensitive resist polymer and at least one organometallic compound of at least one metal selected from the group consisting of yttrium, aluminum, iron, titanium, zirconium and hafnium and mixtures thereof.
Another aspect of the present invention is concerned with a resist composition exhibiting improved resistance to reactive ion etching which comprises a radiation sensitive polymer and at least one filler selected from the group consisting of fused silica, other silicon dioxides, talcum, mica, metals such as aluminum, titanium, copper and nickel, metal oxides such as titanium dioxide, chrome, copper oxide, aluminum oxide, nickel oxide and other metal compounds such as metal nitrides and metal carbides.
Furthermore, the present invention relates to a method for forming a pattern of a radiation sensitive resist which comprises:
a) providing on a substrate a layer of a radiation sensitive resist composition which comprises a radiation sensitive resist polymer and at least one of the above-disclosed fillers;
b) imagewise exposing the layer of resist composition to irradiation; and
c) developing the resist to thereby form the pattern.
In addition, the present invention is concerned with a method for forming a pattern on a substrate which comprises:
a) providing a layer to be patterned on a substrate,
b) providing on the layer to be patterned a layer of a radiation sensitive resist composition which comprises a radiation sensitive resist composition and at least one of the above-disclosed fillers,
c) imagewise exposing the layer of radiation sensitive resist composition to irradiation,
d) developing the resist to form the desired pattern, and
e) subjecting the layer to be patterned to reactive ion etching with the resist acting as a mask to thereby form the desired pattern on the substrate.
Another aspect of the present invention is concerned with a structure comprising a substrate having a patterned layer thereon wherein the patterned layer comprises a radiation sensitive resist polymer and at least one of the above-disclosed fillers.
Still other objects and advantages of the present invention will become readily apparent by those skilled in the art from the following detailed description, wherein it is shown and described only the preferred embodiments of the invention, simply by way of illustration of the best mode contemplated of carrying out the invention. As will be realized the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, without departing from the invention. Accordingly, the description is to be regarded as illustrative in nature and not as restrictive.